Paul Giamatti joins "Downton Abbey"

"Downton Abbey" is adding another American to its cast.

Paul Giamatti has joined the fourth season of the Masterpiece drama, according to TVLine. The actor will play Harold Levinson, Cora's (Elizabeth McGovern) brother in the season 4 finale, alongside Shirley MacLaine who returns as Cora's mother, Martha.

"We're excited that Paul Giamatti will be joining us on 'Downton' to play Cora's brother Harold, the rather free-spirited uncle to Mary and Edith," Gareth Neame, managing director of Carnival Films, said in a statement. "We can't wait to see him work alongside Shirley MacLaine, who are both sure to upset the Grantham's apple cart in this year's finale."

This isn't Giamatti's first time on the small screen. He earned an Emmy and a Golden Globe for his title role in HBO's miniseries "John Adams," and he won't be the only new kid on the "Abbey." He joins fellow new cast members Dame Harriet Walters (as an old friend of Maggie Smith's Dowager), Nigel Harman (as a visiting valet named Green) and Tom Cullen (as a new love interest for Mary).

"Downton Abbey" returns to PBS on Jan. 5.